1. Field of Invention
This invention relates to rotational devices for separating components of a mixture, such as centrifuges.
A separator, by definition, isolates and classifies substances of all types: gases, liquids and solids--according to their physical properties. Various types of separator mechanisms exist including inertial and centrifugal. An inertial separator is a kinetic device that exhibits cyclonic behavior by hydraulically accelerating the mixture to be separated in a circular path and uses the radial acceleration to isolate the components of the mixture. For example, in a hydrocyclone, fluid enters circumferentially at the top and the purified fluid migrates toward the center and out the central tube at the top while the separated denser material tends to stay near the outside wall where it proceeds downward to the underflow port. Separation occurs in a free vortex region.
A centrifugal separator is a kinematic device that achieves separation due to the centrifugal force created by the mechanical rotation of the system. In a conventional centrifuge, fluid normally enters at the center of a whirling mass then is pressed toward the outside by centrifugal force. More dense materials move toward the outside while less dense materials remain on the inside.
One of the problems with commercially available centrifugal separators or centrifuges is that a gradient flow exists to perpetuate eddy currents that cause turbulent mixing of the components of the mixture. This is one of the main reasons why many circulating centrifuges exhibit poor separation efficiencies. The ultra-high rotational speed required to achieve micronic separation of components is evidence of the inefficiency exhibited by commercially available centrifuges.
The residence time provided by conventional centrifuges for components to be separated and to exit the circulating stream is recognized as another serious drawback in current designs. One of the reasons for this inadequacy is that the mixture is introduced near the center of rotation axially where the denser components must travel through the circulating layers of the mixture before they can reach the more stagnant, high energy orbital area near the periphery of the separation chamber--this assumes that a true stagnation zone actually exists in the first place.
Another characteristic of commercial centrifuges is that the less dense components of the mixture are forced to exit near the collection zone for the more dense components or to make abrupt turns at critical points within the system. In many cases, eddy currents are active and there is little control over recontamination of the separated components of the mixture.